<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>边框模型</title>
</head>
<body>
<!--真正决定一个元素的表现形式，是由其边框模型决定的-->
<style>
    .m{
        width: 500px;
        height: 500px;
        border: gray 3px dashed;
        background-color: pink;
        text-align: center;
    }
    .p{
        width: 300px;
        height: 300px;
        border: red 3px dashed;
        background-color: lightgoldenrodyellow;
        text-align: center;
        margin: 100px;
    }
    .w{
        width: 100px;
        height: 100px;
        border: blue 3px solid;
        background-color: lightgoldenrodyellow;
        margin: 100px;
    }
</style>

<div class="m">margin:10px
    <div class="p">padding:5px
        <div class="w">width:70px</div>
    </div>
</div>
</body>
</html>